The invention lies in the area of quality measurement of sound signals, such as audio and voice signals. More in particular, it relates to a method and a device for determining, according to an objective measurement technique, the quality of an output signal from a signal-processing system with respect to a reference signal according to the preamble of claim 1 and claim 7, respectively. A method and a device of such type are known, e.g., from References [1,–,6] (for more bibliographic details on the References, see below under C. References). According to the present known technique, an output signal from an audio or voice signals-processing and/or transporting system, whose signal quality is to be determined, and a reference signal, are mapped on representation signals according to a psycho-physical perception model of the human hearing. As a reference signal, an input signal of the system applied with the output signal obtained may be used, as in References [1,–,5]. But as a reference signal such as, e.g., disclosed in Reference [6], there may also be applied an estimate of the original input signal, reconstructed from the output signal. Subsequently, a differential signal is determined as a function of time from said representation signals, which, according to the model used, is representative of a disturbance sustained in the system present in the output signal. The time-dependent differential signal, hereinafter also referred to as a disturbance signal, may be a difference signal or a ratio signal, or also a combination of both, and constitutes a time-dependent expression for the extent to which, according to the representation model, the output signal deviates from the reference signal. Finally, the disturbance signal is averaged over time, a time-independent quality signal being obtained, which is a measure of the quality of the auditive perception of the output signal.
It is a known phenomenon that, when listening to an audio signal, a short disturbance therein already has a significant influence on the quality perception of the entire signal. This applies not only to spoken words and music, but in general for the reproduction of sound signals. Upon application of the customary linear time averaging, in such cases there is a poor correlation between human quality perception and the quality signal obtained by way of the measurement technique. Application of the “root mean square” as a time-averaging function admittedly provides some improvement, but even then the correlation is still too low for a good operation of the objective method.